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From ka...@apache.org
Subject svn commit: r1548791 [18/22] - in /incubator/helix/site-content: ./ apidocs/reference/org/apache/helix/manager/zk/ helix-admin-webapp/ helix-agent/ helix-core/ helix-examples/ images/ involved/ recipes/ recipes/distributed-lock-manager/ recipes/rabbitm...
Date Sat, 07 Dec 2013 04:21:52 GMT
Added: incubator/helix/site-content/tutorial_propstore.html
URL: http://svn.apache.org/viewvc/incubator/helix/site-content/tutorial_propstore.html?rev=1548791&view=auto
==============================================================================
--- incubator/helix/site-content/tutorial_propstore.html (added)
+++ incubator/helix/site-content/tutorial_propstore.html Sat Dec  7 04:21:43 2013
@@ -0,0 +1,240 @@
+<!DOCTYPE html>
+<!--
+ | Generated by Apache Maven Doxia at 2013-11-07
+ | Rendered using Apache Maven Fluido Skin 1.3.0
+-->
+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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+    <title>Apache Helix -   Tutorial - Application Property Store</title>
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+                  |             <li class="">
+                    <a href="./" title="Apache Helix">
+        Apache Helix</a>
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+      <li class="divider ">/</li>
+        <li class="">  Tutorial - Application Property Store</li>
+                
+                
+                    
+                  <li id="publishDate" class="pull-right">Last Published: 2013-11-07</li> 
+            
+                            </ul>
+      </div>
+
+      
+                
+        <div id="bodyColumn" >
+                                  
+            <!-- -
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
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+to you under the Apache License, Version 2.0 (the
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+
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+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License. --><p></p>
+<h1><a href="./Tutorial.html">Helix Tutorial</a>: Application Property Store</h1>
+<p>In this chapter, we'll learn how to use the application property store.</p>
+<div class="section">
+<div class="section">
+<h3>Property Store<a name="Property_Store"></a></h3>
+<p>It is common that an application needs support for distributed, shared data structures. Helix uses Zookeeper to store the application data and hence provides notifications when the data changes.</p>
+<p>While you could use Zookeeper directly, Helix supports caching the data and a write-through cache. This is far more efficient than reading from Zookeeper for every access.</p>
+<p>See <a href="./apidocs/reference/org/apache/helix/store/package-summary.html">HelixManager.getHelixPropertyStore</a> for details.</p></div></div>
+                  </div>
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\ No newline at end of file

Added: incubator/helix/site-content/tutorial_rebalance.html
URL: http://svn.apache.org/viewvc/incubator/helix/site-content/tutorial_rebalance.html?rev=1548791&view=auto
==============================================================================
--- incubator/helix/site-content/tutorial_rebalance.html (added)
+++ incubator/helix/site-content/tutorial_rebalance.html Sat Dec  7 04:21:43 2013
@@ -0,0 +1,382 @@
+<!DOCTYPE html>
+<!--
+ | Generated by Apache Maven Doxia at 2013-11-07
+ | Rendered using Apache Maven Fluido Skin 1.3.0
+-->
+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+  <head>
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+    <meta name="Date-Revision-yyyymmdd" content="20131107" />
+    <meta http-equiv="Content-Language" content="en" />
+    <title>Apache Helix -   Tutorial - Rebalancing Algorithms</title>
+    <link rel="stylesheet" href="./css/apache-maven-fluido-1.3.0.min.css" />
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+        Apache Helix</a>
+        </li>
+      <li class="divider ">/</li>
+        <li class="">  Tutorial - Rebalancing Algorithms</li>
+                
+                
+                    
+                  <li id="publishDate" class="pull-right">Last Published: 2013-11-07</li> 
+            
+                            </ul>
+      </div>
+
+      
+                
+        <div id="bodyColumn" >
+                                  
+            <!-- -
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License. --><p></p>
+<h1><a href="./Tutorial.html">Helix Tutorial</a>: Rebalancing Algorithms</h1>
+<p>The placement of partitions in a distributed system is essential for the reliability and scalability of the system. For example, when a node fails, it is important that the partitions hosted on that node are reallocated evenly among the remaining nodes. Consistent hashing is one such algorithm that can satisfy this guarantee. Helix provides a variant of consistent hashing based on the RUSH algorithm, among others.</p>
+<p>This means given a number of partitions, replicas and number of nodes, Helix does the automatic assignment of partition to nodes such that:</p>
+
+<ul>
+  
+<li>Each node has the same number of partitions</li>
+  
+<li>Replicas of the same partition do not stay on the same node</li>
+  
+<li>When a node fails, the partitions will be equally distributed among the remaining nodes</li>
+  
+<li>When new nodes are added, the number of partitions moved will be minimized along with satisfying the above criteria</li>
+</ul>
+<p>Helix employs a rebalancing algorithm to compute the <i>ideal state</i> of the system. When the <i>current state</i> differs from the <i>ideal state</i>, Helix uses it as the target state of the system and computes the appropriate transitions needed to bring it to the <i>ideal state</i>.</p>
+<p>Helix makes it easy to perform this operation, while giving you control over the algorithm. In this section, we'll see how to implement the desired behavior.</p>
+<p>Helix has four options for rebalancing, in increasing order of customization by the system builder:</p>
+
+<ul>
+  
+<li>FULL_AUTO</li>
+  
+<li>SEMI_AUTO</li>
+  
+<li>CUSTOMIZED</li>
+  
+<li>USER_DEFINED</li>
+</ul>
+
+<div class="source">
+<pre>            |FULL_AUTO     |  SEMI_AUTO | CUSTOMIZED|  USER_DEFINED  |
+            ---------------------------------------------------------|
+   LOCATION | HELIX        |  APP       |  APP      |      APP       |
+            ---------------------------------------------------------|
+      STATE | HELIX        |  HELIX     |  APP      |      APP       |
+            ----------------------------------------------------------
+</pre></div>
+<div class="section">
+<div class="section">
+<h3>FULL_AUTO<a name="FULL_AUTO"></a></h3>
+<p>When the rebalance mode is set to FULL_AUTO, Helix controls both the location of the replica along with the state. This option is useful for applications where creation of a replica is not expensive. </p>
+<p>For example, consider this system that uses a MasterSlave state model, with 3 partitions and 2 replicas in the ideal state.</p>
+
+<div class="source">
+<pre>{
+  &quot;id&quot; : &quot;MyResource&quot;,
+  &quot;simpleFields&quot; : {
+    &quot;REBALANCE_MODE&quot; : &quot;FULL_AUTO&quot;,
+    &quot;NUM_PARTITIONS&quot; : &quot;3&quot;,
+    &quot;REPLICAS&quot; : &quot;2&quot;,
+    &quot;STATE_MODEL_DEF_REF&quot; : &quot;MasterSlave&quot;,
+  }
+  &quot;listFields&quot; : {
+    &quot;MyResource_0&quot; : [],
+    &quot;MyResource_1&quot; : [],
+    &quot;MyResource_2&quot; : []
+  },
+  &quot;mapFields&quot; : {
+  }
+}
+</pre></div>
+<p>If there are 3 nodes in the cluster, then Helix will balance the masters and slaves equally. The ideal state is therefore:</p>
+
+<div class="source">
+<pre>{
+  &quot;id&quot; : &quot;MyResource&quot;,
+  &quot;simpleFields&quot; : {
+    &quot;NUM_PARTITIONS&quot; : &quot;3&quot;,
+    &quot;REPLICAS&quot; : &quot;2&quot;,
+    &quot;STATE_MODEL_DEF_REF&quot; : &quot;MasterSlave&quot;,
+  },
+  &quot;mapFields&quot; : {
+    &quot;MyResource_0&quot; : {
+      &quot;N1&quot; : &quot;MASTER&quot;,
+      &quot;N2&quot; : &quot;SLAVE&quot;,
+    },
+    &quot;MyResource_1&quot; : {
+      &quot;N2&quot; : &quot;MASTER&quot;,
+      &quot;N3&quot; : &quot;SLAVE&quot;,
+    },
+    &quot;MyResource_2&quot; : {
+      &quot;N3&quot; : &quot;MASTER&quot;,
+      &quot;N1&quot; : &quot;SLAVE&quot;,
+    }
+  }
+}
+</pre></div>
+<p>Another typical example is evenly distributing a group of tasks among the currently healthy processes. For example, if there are 60 tasks and 4 nodes, Helix assigns 15 tasks to each node. When one node fails, Helix redistributes its 15 tasks to the remaining 3 nodes, resulting in a balanced 20 tasks per node. Similarly, if a node is added, Helix re-allocates 3 tasks from each of the 4 nodes to the 5th node, resulting in a balanced distribution of 12 tasks per node.. </p>
+<div class="section">
+<h4>SEMI_AUTO<a name="SEMI_AUTO"></a></h4>
+<p>When the application needs to control the placement of the replicas, use the SEMI_AUTO rebalance mode.</p>
+<p>Example: In the ideal state below, the partition 'MyResource_0' is constrained to be placed only on node1 or node2. The choice of <i>state</i> is still controlled by Helix. That means MyResource_0.MASTER could be on node1 and MyResource_0.SLAVE on node2, or vice-versa but neither would be placed on node3.</p>
+
+<div class="source">
+<pre>{
+  &quot;id&quot; : &quot;MyResource&quot;,
+  &quot;simpleFields&quot; : {
+    &quot;REBALANCE_MODE&quot; : &quot;SEMI_AUTO&quot;,
+    &quot;NUM_PARTITIONS&quot; : &quot;3&quot;,
+    &quot;REPLICAS&quot; : &quot;2&quot;,
+    &quot;STATE_MODEL_DEF_REF&quot; : &quot;MasterSlave&quot;,
+  }
+  &quot;listFields&quot; : {
+    &quot;MyResource_0&quot; : [node1, node2],
+    &quot;MyResource_1&quot; : [node2, node3],
+    &quot;MyResource_2&quot; : [node3, node1]
+  },
+  &quot;mapFields&quot; : {
+  }
+}
+</pre></div>
+<p>The MasterSlave state model requires that a partition has exactly one MASTER at all times, and the other replicas should be SLAVEs. In this simple example with 2 replicas per partition, there would be one MASTER and one SLAVE. Upon failover, a SLAVE has to assume mastership, and a new SLAVE will be generated.</p>
+<p>In this mode when node1 fails, unlike in FULL_AUTO mode the partition is <i>not</i> moved from node1 to node3. Instead, Helix will decide to change the state of MyResource_0 on node2 from SLAVE to MASTER, based on the system constraints. </p></div>
+<div class="section">
+<h4>CUSTOMIZED<a name="CUSTOMIZED"></a></h4>
+<p>Helix offers a third mode called CUSTOMIZED, in which the application controls the placement <i>and</i> state of each replica. The application needs to implement a callback interface that Helix invokes when the cluster state changes. Within this callback, the application can recompute the idealstate. Helix will then issue appropriate transitions such that <i>Idealstate</i> and <i>Currentstate</i> converges.</p>
+<p>Here's an example, again with 3 partitions, 2 replicas per partition, and the MasterSlave state model:</p>
+
+<div class="source">
+<pre>{
+  &quot;id&quot; : &quot;MyResource&quot;,
+  &quot;simpleFields&quot; : {
+    &quot;REBALANCE_MODE&quot; : &quot;CUSTOMIZED&quot;,
+    &quot;NUM_PARTITIONS&quot; : &quot;3&quot;,
+    &quot;REPLICAS&quot; : &quot;2&quot;,
+    &quot;STATE_MODEL_DEF_REF&quot; : &quot;MasterSlave&quot;,
+  },
+  &quot;mapFields&quot; : {
+    &quot;MyResource_0&quot; : {
+      &quot;N1&quot; : &quot;MASTER&quot;,
+      &quot;N2&quot; : &quot;SLAVE&quot;,
+    },
+    &quot;MyResource_1&quot; : {
+      &quot;N2&quot; : &quot;MASTER&quot;,
+      &quot;N3&quot; : &quot;SLAVE&quot;,
+    },
+    &quot;MyResource_2&quot; : {
+      &quot;N3&quot; : &quot;MASTER&quot;,
+      &quot;N1&quot; : &quot;SLAVE&quot;,
+    }
+  }
+}
+</pre></div>
+<p>Suppose the current state of the system is &#x2018;MyResource_0&#x2019; -&gt; {N1:MASTER, N2:SLAVE} and the application changes the ideal state to &#x2018;MyResource_0&#x2019; -&gt; {N1:SLAVE,N2:MASTER}. While the application decides which node is MASTER and which is SLAVE, Helix will not blindly issue MASTER&#x2013;&gt;SLAVE to N1 and SLAVE&#x2013;&gt;MASTER to N2 in parallel, since that might result in a transient state where both N1 and N2 are masters, which violates the MasterSlave constraint that there is exactly one MASTER at a time. Helix will first issue MASTER&#x2013;&gt;SLAVE to N1 and after it is completed, it will issue SLAVE&#x2013;&gt;MASTER to N2. </p></div>
+<div class="section">
+<h4>USER_DEFINED<a name="USER_DEFINED"></a></h4>
+<p>For maximum flexibility, Helix exposes an interface that can allow applications to plug in custom rebalancing logic. By providing the name of a class that implements the Rebalancer interface, Helix will automatically call the contained method whenever there is a change to the live participants in the cluster. For more, see <a href="./tutorial_user_def_rebalancer.html">User-Defined Rebalancer</a>.</p></div>
+<div class="section">
+<h4>Backwards Compatibility<a name="Backwards_Compatibility"></a></h4>
+<p>In previous versions, FULL_AUTO was called AUTO_REBALANCE and SEMI_AUTO was called AUTO. Furthermore, they were presented as the IDEAL_STATE_MODE. Helix supports both IDEAL_STATE_MODE and REBALANCE_MODE, but IDEAL_STATE_MODE is now deprecated and may be phased out in future versions.</p></div></div></div>
+                  </div>
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+
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+
+    <footer>
+            <div class="container">
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+                        <a href="http://www.apache.org/">The Apache Software Foundation</a>.
+            All Rights Reserved.      
+                    
+      </div>
+
+                                                                  <?xml version="1.0" encoding="UTF-8"?>
+<div class="row span16">
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+        All other marks mentioned may be trademarks or registered trademarks of their respective owners.</div>
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Added: incubator/helix/site-content/tutorial_spectator.html
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==============================================================================
--- incubator/helix/site-content/tutorial_spectator.html (added)
+++ incubator/helix/site-content/tutorial_spectator.html Sat Dec  7 04:21:43 2013
@@ -0,0 +1,290 @@
+<!DOCTYPE html>
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+        Apache Helix</a>
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+      <li class="divider ">/</li>
+        <li class="">  Tutorial - Spectator</li>
+                
+                
+                    
+                  <li id="publishDate" class="pull-right">Last Published: 2013-11-07</li> 
+            
+                            </ul>
+      </div>
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+Licensed to the Apache Software Foundation (ASF) under one
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+
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+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License. --><p></p>
+<h1><a href="./Tutorial.html">Helix Tutorial</a>: Spectator</h1>
+<p>Next, we'll learn how to implement a Spectator. Typically, a spectator needs to react to changes within the distributed system. Examples: a client that needs to know where to send a request, a topic consumer in a consumer group. The spectator is automatically informed of changes in the <i>external state</i> of the cluster, but it does not have to add any code to keep track of other components in the system.</p>
+<div class="section">
+<div class="section">
+<h3>Start the Helix agent<a name="Start_the_Helix_agent"></a></h3>
+<p>Same as for a Participant, The Helix agent is the common component that connects each system component with the controller.</p>
+<p>It requires the following parameters:</p>
+
+<ul>
+  
+<li>clusterName: A logical name to represent the group of nodes</li>
+  
+<li>instanceName: A logical name of the process creating the manager instance. Generally this is host:port.</li>
+  
+<li>instanceType: Type of the process. This can be one of the following types, in this case, use SPECTATOR:
+  
+<ul>
+    
+<li>CONTROLLER: Process that controls the cluster, any number of controllers can be started but only one will be active at any given time.</li>
+    
+<li>PARTICIPANT: Process that performs the actual task in the distributed system.</li>
+    
+<li>SPECTATOR: Process that observes the changes in the cluster.</li>
+    
+<li>ADMIN: To carry out system admin actions.</li>
+  </ul></li>
+  
+<li>zkConnectString: Connection string to Zookeeper. This is of the form host1:port1,host2:port2,host3:port3.</li>
+</ul>
+<p>After the Helix manager instance is created, only thing that needs to be registered is the listener. When the ExternalView changes, the listener is notified.</p></div>
+<div class="section">
+<h3>Spectator Code<a name="Spectator_Code"></a></h3>
+<p>A spectator observes the cluster and is notified when the state of the system changes. Helix consolidates the state of entire cluster in one Znode called ExternalView. Helix provides a default implementation RoutingTableProvider that caches the cluster state and updates it when there is a change in the cluster.</p>
+
+<div class="source">
+<pre>manager = HelixManagerFactory.getZKHelixManager(clusterName,
+                                                          instanceName,
+                                                          InstanceType.PARTICIPANT,
+                                                          zkConnectString);
+manager.connect();
+RoutingTableProvider routingTableProvider = new RoutingTableProvider();
+manager.addExternalViewChangeListener(routingTableProvider);
+</pre></div>
+<p>In the following code snippet, the application sends the request to a valid instance by interrogating the external view. Suppose the desired resource for this request is in the partition myDB_1.</p>
+
+<div class="source">
+<pre>## instances = routingTableProvider.getInstances(, &quot;PARTITION_NAME&quot;, &quot;PARTITION_STATE&quot;);
+instances = routingTableProvider.getInstances(&quot;myDB&quot;, &quot;myDB_1&quot;, &quot;ONLINE&quot;);
+
+////////////////////////////////////////////////////////////////////////////////////////////////
+// Application-specific code to send a request to one of the instances                        //
+////////////////////////////////////////////////////////////////////////////////////////////////
+
+theInstance = instances.get(0);  // should choose an instance and throw an exception if none are available
+result = theInstance.sendRequest(yourApplicationRequest, responseObject);
+
+</pre></div>
+<p>When the external view changes, the application needs to react by sending requests to a different instance. </p></div></div>
+                  </div>
+          </div>
+
+    <hr/>
+
+    <footer>
+            <div class="container">
+              <div class="row span12">Copyright &copy;                    2013
+                        <a href="http://www.apache.org/">The Apache Software Foundation</a>.
+            All Rights Reserved.      
+                    
+      </div>
+
+                                                                  <?xml version="1.0" encoding="UTF-8"?>
+<div class="row span16">
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Added: incubator/helix/site-content/tutorial_state.html
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==============================================================================
--- incubator/helix/site-content/tutorial_state.html (added)
+++ incubator/helix/site-content/tutorial_state.html Sat Dec  7 04:21:43 2013
@@ -0,0 +1,348 @@
+<!DOCTYPE html>
+<!--
+ | Generated by Apache Maven Doxia at 2013-11-07
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+                  |             <li class="">
+                    <a href="./" title="Apache Helix">
+        Apache Helix</a>
+        </li>
+      <li class="divider ">/</li>
+        <li class="">  Tutorial - State Machine Configuration</li>
+                
+                
+                    
+                  <li id="publishDate" class="pull-right">Last Published: 2013-11-07</li> 
+            
+                            </ul>
+      </div>
+
+      
+                
+        <div id="bodyColumn" >
+                                  
+            <!-- -
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License. --><p></p>
+<h1><a href="./Tutorial.html">Helix Tutorial</a>: State Machine Configuration</h1>
+<p>In this chapter, we'll learn about the state models provided by Helix, and how to create your own custom state model.</p>
+<div class="section">
+<h2>State Models<a name="State_Models"></a></h2>
+<p>Helix comes with 3 default state models that are commonly used. It is possible to have multiple state models in a cluster. Every resource that is added should be configured to use a state model that govern its <i>ideal state</i>.</p>
+<div class="section">
+<h3>MASTER-SLAVE<a name="MASTER-SLAVE"></a></h3>
+
+<ul>
+  
+<li>3 states: OFFLINE, SLAVE, MASTER</li>
+  
+<li>Maximum number of masters: 1</li>
+  
+<li>Slaves are based on the replication factor. The replication factor can be specified while adding the resource.</li>
+</ul></div>
+<div class="section">
+<h3>ONLINE-OFFLINE<a name="ONLINE-OFFLINE"></a></h3>
+
+<ul>
+  
+<li>Has 2 states: OFFLINE and ONLINE. This simple state model is a good starting point for most applications.</li>
+</ul></div>
+<div class="section">
+<h3>LEADER-STANDBY<a name="LEADER-STANDBY"></a></h3>
+
+<ul>
+  
+<li>1 Leader and multiple stand-bys. The idea is that exactly one leader accomplishes a designated task, the stand-bys are ready to take over if the leader fails.</li>
+</ul></div></div>
+<div class="section">
+<h2>Constraints<a name="Constraints"></a></h2>
+<p>In addition to the state machine configuration, one can specify the constraints of states and transitions.</p>
+<p>For example, one can say:</p>
+
+<ul>
+  
+<li>
+<p>MASTER:1 <br />Maximum number of replicas in MASTER state at any time is 1</p></li>
+  
+<li>
+<p>OFFLINE-SLAVE:5 <br />Maximum number of OFFLINE-SLAVE transitions that can happen concurrently in the system is 5 in this example.</p></li>
+</ul>
+<div class="section">
+<h3>Dynamic State Constraints<a name="Dynamic_State_Constraints"></a></h3>
+<p>We also support two dynamic upper bounds for the number of replicas in each state:</p>
+
+<ul>
+  
+<li>N: The number of replicas in the state is at most the number of live participants in the cluster</li>
+  
+<li>R: The number of replicas in the state is at most the specified replica count for the partition</li>
+</ul></div>
+<div class="section">
+<h3>State Priority<a name="State_Priority"></a></h3>
+<p>Helix uses a greedy approach to satisfy the state constraints. For example, if the state machine configuration says it needs 1 MASTER and 2 SLAVES, but only 1 node is active, Helix must promote it to MASTER. This behavior is achieved by providing the state priority list as [MASTER, SLAVE].</p></div>
+<div class="section">
+<h3>State Transition Priority<a name="State_Transition_Priority"></a></h3>
+<p>Helix tries to fire as many transitions as possible in parallel to reach the stable state without violating constraints. By default, Helix simply sorts the transitions alphabetically and fires as many as it can without violating the constraints. You can control this by overriding the priority order.</p></div></div>
+<div class="section">
+<h2>Special States<a name="Special_States"></a></h2>
+<div class="section">
+<h3>DROPPED<a name="DROPPED"></a></h3>
+<p>The DROPPED state is used to signify a replica that was served by a given participant, but is no longer served. This allows Helix and its participants to effectively clean up. There are two requirements that every new state model should follow with respect to the DROPPED state:</p>
+
+<ul>
+  
+<li>The DROPPED state must be defined</li>
+  
+<li>There must be a path to DROPPED for every state in the model</li>
+</ul></div>
+<div class="section">
+<h3>ERROR<a name="ERROR"></a></h3>
+<p>The ERROR state is used whenever the participant serving a partition encountered an error and cannot continue to serve the partition. HelixAdmin has &quot;reset&quot; functionality to allow for participants to recover from the ERROR state.</p></div></div>
+<div class="section">
+<h2>Annotated Example<a name="Annotated_Example"></a></h2>
+<p>Below is a complete definition of a Master-Slave state model. Notice the fields marked REQUIRED; these are essential for any state model definition.</p>
+
+<div class="source">
+<pre>StateModelDefinition stateModel = new StateModelDefinition.Builder(&quot;MasterSlave&quot;)
+  // OFFLINE is the state that the system starts in (initial state is REQUIRED)
+  .initialState(&quot;OFFLINE&quot;)
+
+  // Lowest number here indicates highest priority, no value indicates lowest priority
+  .addState(&quot;MASTER&quot;, 1)
+  .addState(&quot;SLAVE&quot;, 2)
+  .addState(&quot;OFFLINE&quot;)
+
+  // Note the special inclusion of the DROPPED state (REQUIRED)
+  .addState(HelixDefinedState.DROPPED.toString())
+
+  // No more than one master allowed
+  .upperBound(&quot;MASTER&quot;, 1)
+
+  // R indicates an upper bound of number of replicas for each partition
+  .dynamicUpperBound(&quot;SLAVE&quot;, &quot;R&quot;)
+
+  // Add some high-priority transitions
+  .addTransition(&quot;SLAVE&quot;, &quot;MASTER&quot;, 1)
+  .addTransition(&quot;OFFLINE&quot;, &quot;SLAVE&quot;, 2)
+
+  // Using the same priority value indicates that these transitions can fire in any order
+  .addTransition(&quot;MASTER&quot;, &quot;SLAVE&quot;, 3)
+  .addTransition(&quot;SLAVE&quot;, &quot;OFFLINE&quot;, 3)
+
+  // Not specifying a value defaults to lowest priority
+  // Notice the inclusion of the OFFLINE to DROPPED transition
+  // Since every state has a path to OFFLINE, they each now have a path to DROPPED (REQUIRED)
+  .addTransition(&quot;OFFLINE&quot;, HelixDefinedState.DROPPED.toString())
+
+  // Create the StateModelDefinition instance
+  .build();
+
+  // Use the isValid() function to make sure the StateModelDefinition will work without issues
+  Assert.assertTrue(stateModel.isValid());
+</pre></div></div>
+                  </div>
+          </div>
+
+    <hr/>
+
+    <footer>
+            <div class="container">
+              <div class="row span12">Copyright &copy;                    2013
+                        <a href="http://www.apache.org/">The Apache Software Foundation</a>.
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URL: http://svn.apache.org/viewvc/incubator/helix/site-content/tutorial_throttling.html?rev=1548791&view=auto
==============================================================================
--- incubator/helix/site-content/tutorial_throttling.html (added)
+++ incubator/helix/site-content/tutorial_throttling.html Sat Dec  7 04:21:43 2013
@@ -0,0 +1,250 @@
+<!DOCTYPE html>
+<!--
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+                    <a href="./" title="Apache Helix">
+        Apache Helix</a>
+        </li>
+      <li class="divider ">/</li>
+        <li class="">  Tutorial - Throttling</li>
+                
+                
+                    
+                  <li id="publishDate" class="pull-right">Last Published: 2013-11-07</li> 
+            
+                            </ul>
+      </div>
+
+      
+                
+        <div id="bodyColumn" >
+                                  
+            <!-- -
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
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+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License. --><p></p>
+<h1><a href="./Tutorial.html">Helix Tutorial</a>: Throttling</h1>
+<p>In this chapter, we'll learn how to control the parallel execution of cluster tasks. Only a centralized cluster manager with global knowledge is capable of coordinating this decision.</p>
+<div class="section">
+<div class="section">
+<h3>Throttling<a name="Throttling"></a></h3>
+<p>Since all state changes in the system are triggered through transitions, Helix can control the number of transitions that can happen in parallel. Some of the transitions may be light weight, but some might involve moving data, which is quite expensive from a network and iops perspective.</p>
+<p>Helix allows applications to set a threshold on transitions. The threshold can be set at multiple scopes:</p>
+
+<ul>
+  
+<li>MessageType e.g STATE_TRANSITION</li>
+  
+<li>TransitionType e.g SLAVE-MASTER</li>
+  
+<li>Resource e.g database</li>
+  
+<li>Node i.e per-node maximum transitions in parallel</li>
+</ul></div></div>
+                  </div>
+          </div>
+
+    <hr/>
+
+    <footer>
+            <div class="container">
+              <div class="row span12">Copyright &copy;                    2013
+                        <a href="http://www.apache.org/">The Apache Software Foundation</a>.
+            All Rights Reserved.      
+                    
+      </div>
+
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+<div class="row span16">
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